In order to transmit and receive data between semiconductor integrated circuits through a small number of data transmission lines, the techniques of serial data transmission are used. As the techniques of serial data transmission, a scheme of transmitting serial data and a clock signal through separate respective transmission lines and a scheme of superimposing a clock signal on serial data have been known.
The former scheme, which is also referred to as a clock synchronization scheme, may be employed, for example, in a low voltage differential signaling (LVDS) bus, and an inter IC (I2C) bus. In this scheme, however, synchronization between the clock signal and the serial data may be lost due to an influence of jitter of the clock signal or a difference in propagation delays between the serial data and the clock signal so that it is difficult to transmit the data at a high speed exceeding 1 Gbps.
In contrast, the scheme of superimposing the clock signal on the serial data, in a transmission circuit, the serial data is encoded such that bits are changed according to a predetermined rule. A reception circuit reproduces the clock signal embedded in the serial data. In this sense, this scheme is also referred to as a CDR (Clock Data Recovery) scheme. In the CDR scheme, synchronization between the serial data and the clock signal can be maintained so that a higher transfer rate may be realized.
In order to solve the problem of electromagnetic interference (EMI) caused in the serial data transmission, a transmitter may scramble the serial data and randomize the serial data propagating through a transmission channel, thereby spreading a spectrum in the related art.
FIG. 1 shows a data format for a conventional serial data transmission adopting the scrambling. A smallest unit of data is called 1 word. In case of using an 8B10B coding scheme, 1 word is 10 bits, 8 bits of which are data corresponding to information and remaining 2 bits of which are redundancy bits for embedding the clock signal.
Image data (pixel data) may be scrambled and subsequently 8B10B coded to generate a word called a D symbol. Scramble controlling codes (K symbols) are respectively arranged at an equal interval for a plurality of D symbols. For example, each K symbol may be inserted once every ten words.
The transmission circuit may generate a pseudorandom number changing at a predetermined cycle (e.g., every one word) and performs scrambling on the image data with the pseudorandom number. The K symbols may include a first (initialization) code K0 and a second code (synchronization code) K1. The initialization code K0 may be inserted one time for each scrambling period (e.g., every 1000 words). The initialization code K0 may indicate the beginning of generating a pseudorandom number. The remaining K symbols may be allocated to the synchronization code K1.
The reception circuit may be synchronized with the transmission circuit by referring to the K symbols so that it generates the same pseudorandom number as the pseudorandom number generated by the transmission circuit and descrambles the received data using the generated pseudorandom number.
Here, if the transmission circuit and the reception circuit lose synchronization, the pseudorandom numbers generated by the transmission circuit and the reception circuit are not identical, and thus, descrambling may not be correctly performed. That is, when the synchronization is lost in the middle of a scrambling period, a reception error occurs.
The synchronization code K1 may be included once for every 10 words. Thus, even in a case in which the transmission circuit and the reception circuit lose synchronization, if a synchronization shift occurs within the front and rear 5 words, a current correct word position may be known by normally receiving the next synchronization code K1 so that the synchronization may be reestablished and the pseudorandom number may also be returned to a correct value. However, if the synchronization shift exceeds the front and rear 5 words, a correct word position may not be restored in spite of using the synchronization code K1 so that the synchronization error continues until the next initialization code K0 is correctly received.
For example, in an electronic device including a display panel, the serial data transmission may be used in transmitting image data from a frame memory storing the image data (which includes a video and a still image) to a driver circuit of the display panel. In a case where scrambling is performed for each line of image data as a unit period, when a synchronization error exceeding 10 words occurs in the middle of data transmission of a certain line, subsequent image data in that line may not be correctly displayed, which causes disturbance of an image recognized by a user.